How to use diodes to drop voltage

Written by tracy underwood

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Diode forward drop can be used to a circuit builder's advantage. (Stockbyte/Valueline/Getty Images)

Electronics hobbyists are familiar with the use of zener diodes to reduce voltage to a circuit. Another common means of dropping voltage is a series resistance. But a resistor presents varying voltage to the circuit as the current varies, and this can cause overvoltage stress to components. Common silicon diodes can be used to drop voltage to the proper level for a circuit, using the forward voltage drop inherent in all diodes.

Skill level:

Moderately Easy

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Things you need

Multimeter

Power supply

Silicon diodes

Soldering iron

Solder

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Instructions

1

Set the multimeter for voltage reading and measure the resting output voltage of the power supply. Compare this voltage to the desired circuit voltage. For example, if the supply outputs 12.7 volts and the circuit is rated 9 volts, the difference is 3.7 volts.

2

Set the multimeter for diode check and measure the forward drop of the diodes. Most silicon diodes will measure approximately .7 volt.

3

Divide the desired voltage drop by the measured forward drop per diode. Round up to the next whole number. In the example given, 3.7 volts divided by .7 volt equals 5.29; rounded up, it's 6. This number indicates how many diodes to connect to the circuit.

4

Connect the calculated number of diodes in series and forward biased. Solder all connections.

5

Connect the diode string in series forward biased between the power supply and the circuit.